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Just a thought on the comment the viruses evolving to be less lethal. Stann mentioned that Polio is quite lethal and has been around for a long time and he used this as an example. However it’s my understanding from TWiV that before humanity started using basic hygine that Polio was not a major issue as children got it when they were very young and the subsequent brain swelling was not an issue as skulls at that age still have a fair bit of movement in them. So really Polio in its more lethal form to us has not been around a long time.

The point Stann brings up is really interesting though. After a bit more thought I think I’ve got an interesting idea. Just as there is no evolutionary pressure in the human genome to get rid of the ‘junk DNA’ there is no major pressure for viruses to get rid of their lethality as long as they can be transmitted. However if they become less lethal this can help them transmit to a larger degree as the hosts have more time to transmit the virus.

This is an evolutionary niche that the virus can move into and take advantage of. While slowly displacing the more lethal version of itself over a very long time period.

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